FLUORESCENCE DEPOLARIZATION STUDY ON LOCAL MOTIONS OF ANTHRACENE-LABELED POLY(ALKYL METHACRYLATE)S IN DILUTE-SOLUTIONS AND EVALUATION OF THEIR CHAIN STIFFNESS

Samples of Poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), and poly(isopropyl methacrylate) (PiPMA) labeled with anthracene in the middle of the backbone chain were synthesized, and their local motions in dilute solutions were investigated by the fluorescence depolarization technique. Both the static stiffness parameter s-1 and the mean relaxation time T(m) as a measure of the dynamic chain stiffness were evaluated from the time-resolved data of fluorescence anisotropy ratio, and a correlation between these two parameters was found. Conformational energy calculations were performed for the diad compounds of PMMA, PEMA, and PiPMA, and then, the characteristic ratios were calculated according to the rotational isomeric state (RIS) model. The static chain stiffness parameter lambda-1 was obtained for the above three polymers as an independent evaluation of the static chain stiffness by a comparison between the RIS model and the helical wormlike chain model established by Yamakawa and his co-workers, and a correlation between lambda-1 and T(m) was also found. The conformational character of PiPMA is remarkably different from that of PMMA and PEMA, resulting in greater chain stiffness for PiPMA than for PMMA and PEMA.